This invention relates to a tilt control device for an optical disk device including an optical disk recording device, an optical disk reproduction device, an optical disk recording and reproduction device and a photomagnetic disk device and, more particularly, to a tilt control device for an optical disk device capable of performing a stable tilt control during a search operation.
In an optical disk device, when a tilt exists in an optical disk, an optical axis of an objective lens of an optical pickup does not cross perpendicularly with a recording surface of the optical disk with resulting deterioration in the quality of a recorded or reproduced signal. A tilt control device is provided for correct a tilt between the optical axis of the optical pickup and direction perpendicular to the recording surface of the optical disk at a position where the optical axis of the optical pickup crosses with the recording surface. The tilt control device includes a tilt actuator which drives the optical pickup in a radial tilt direction and a tilt sensor which detects a tilt in the radial tilt direction (a tilt error) between the optical axis of the optical pickup and the direction perpendicular to the recording surface of the optical disk and constitutes a servo circuit for driving the tilt actuator so as to reduce the tilt error to zero at a recording or reproduction position.
In the tilt control device, a servo area is normally restricted to a certain narrow area for preventing response of the servo system to a surface undulation of the optical disk, i.e., a swell in the circumferential direction of the optical disk. For this reason, when a search for a desired target position on the optical disk is made by moving the optical disk at a high speed in the radial direction of the disk (i.e., a high speed search), the tilt servo cannot follow up variation in the tilt of the disk and, as a result, notwithstanding that the optical pickup has reached a zone in the vicinity of the target position, the tracking servo cannot immediately be brought into a locked state or, in the worst case, the focus servo comes out of lock, so that it sometimes requires a relatively long time before recording or reproduction at the target position is started.
It is, therefore, an object of the invention to provide a tilt control device which has eliminated the above described disadvantage of the prior art tilt control device and is capable of realizing a stable tilt control during a high speed search.